Plasma-Assisted construction of waterfall-type IEF in N-TiO2/WO3 S-scheme heterojunction for efficient Visible-Light-Driven degradation of Cl-VOCs

Abstract

Constructing S-scheme heterojunctions with a robust internal electric field (IEF) to enhance the photocatalytic degradation of chlorinated volatile organic compounds (Cl-VOCs) presents a significant challenge. Herein, an innovative S-scheme heterojunction of N-doped titanium dioxide (TiO₂) and tungsten trioxide (WO₃) with abundant oxygen vacancies (OVs) was first synthesized and manipulated via an eco-friendly two-step plasma. The charge transfer pathway between TiO₂ and WO₃ was analyzed using UV–Vis DRS, XPS, UPS, and EPR measurements, confirming the successful formation of the S-scheme heterojunction. Interestingly, two novel types of IEF: stream-type and waterfall-type were first proposed to distinguish the IEF strength before and after regulation. Under visible light, 5NTW with the optimal ratio (4.66 at% nitrogen and 5 wt% WO₃) achieved the highest degradation efficiency and carbon dioxide mineralization rate of 95.4% and 94.1% for chlorobenzene, respectively. The performance enhancement was attributed to the fact that N-doping modifies the electronic structure and work function of TiO₂, enhancing the Fermi level difference (ΔE_f) with WO₃. Meanwhile, the plasma treatment roughened the surface topography of the catalyst and increased the content of OVs, which serve as charge traps and bolster active sites. These synergies led to a transformation from a stream-type IEF of TW to a waterfall-type IEF of 5NTW. KPFM, zeta potential tests, and DFT calculations confirmed that the IEF strength and the number of electron transfers in the waterfall-type IEF are 3.17 and 2.04 times greater, respectively, than those in the stream-type IEF. This strategy transcends the limitations of previous work, offering a novel perspective on the integrated optimization of photocatalysts for superior performance and also further broadens the application prospects of nonthermal plasma technology.